Polycrystalline diamond (PCD) material and polycrystalline cubic boron nitride (PCBN) material are examples of polycrystalline super-hard materials. As used herein, super-hard materials have a Vickers hardness of at least about 28 GPa.
PCD material comprises a mass of substantially inter-grown diamond grains and interstices between the diamond grains. PCD may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure and temperature in the presence of a sintering aid such as cobalt, which may promote the inter-growth of diamond grains. The sintering aid may also be referred to as a catalyst material for diamond. Interstices within the PCD material may be wholly or partially filled with residual catalyst material. PCD may typically be integrally formed on and bonded to a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for sintering the PCD. Tool inserts comprising PCD material are widely used in drill bits used for boring into the earth in the oil and gas drilling industry. Various grades of PCD having various compositions and microstructure are known and important properties such as the Young's modulus and strength of the PCD material may depend on its composition and microstructure, including the size distribution, homogeneity and contiguity of the diamond grains of which the PCD material is comprised. In practice, the grade of PCD produced may be constrained by the composition and micro-structural characteristics of the carbide substrate on which it is formed.
U.S. Pat. No. 7,533,740 discloses a cutting element in which thermally stable PCD layer is mechanically locked to a substrate. U.S. Pat. No. 4,382,477 discloses a support stud assembly mounted onto a drill bit, in which a hard preform is held to a support stud by means of a peg and a leaf spring.
There is a need to provide robust cutter inserts particularly but not exclusively for drill bits for boring into rock, permitting flexibility in the combination of various grades or configurations of super-hard structures and support substrates.